Thermohydraulic modelling framework for pressure–property–performance analysis of organic fluids in Direct Vapour Generation

Efficient phase-change heat transfer, governed by fluid thermophysical properties, is essential for advancing renewable energy technologies. In solar thermal systems employing Direct Vapour Generation (DVG), organic working fluids offer distinct advantages, yet their boiling behaviour under varying pressures remains insufficiently characterised. This study extends a validated non-iterative thermohydraulic model, originally developed for steam, to simulate pressure-dependent boiling of six low global warming potential refrigerants–R1233zd(E), R1234ze(Z), R245fa, R123, R113, and MM–in horizontal receiver tubes. The framework quantitatively links thermophysical property variation with operating pressure to DVG performance metrics. Increasing pressure from 0.7 P crit to 0.9 P crit shortens boiling length by 49%–58%, reduces pressure drop by 76%–89%, and suppresses temperature glide by 81%–88%. These enhancements arise from a combination of the reduced latent heat of vaporisation (accounting for a substantial portion of the effect) and pressure-induced changes in thermophysical properties such as liquid viscosity and thermal conductivity, which drive an additional 9%–18% improvement in phase-change efficiency. Flow regime predictions indicate annular flow stabilisation at higher pressures, mitigating stratification risks and sustaining a high heat transfer rate. The approach employs pressure-explicit phase-change functions and Taitel–Dukler flow mapping, eliminating iterative calculations and enabling property-driven optimisation of organic fluids for solar thermal power and other renewable phase-change applications. • Solar direct vapour generation with organic fluids. • Boiling length reduced by 49%–58% at higher pressures. • Pressure drop suppressed by 76%–89% near critical point. • Higher pressure stabilises annular flow, boosting efficiency. • Property-driven analysis of low-GWP organic fluids.